Starters for prime movers such as gas turbines



Jan. 1, 1957 RANDALL 2,775,866

STARTERS FOR PRIME MOVERS SUCH AS GAS TURBINES Original Filed June 4, 1952 //v l/EN TOR hf N/VE TH BflRR/NGTON RANDALL /7 T TOIFA/E Y United States Patent STARTERS FOR PRIME MoyERsst-JC-nas GAS TURBINES H Kenneth Bar'ring'tonRandall,(Ioventi'y,*Engla!id, iissignor to The British Thomson-Houston Company Limited, a British company This invention relates to starters for gas turbines and the like and is more particularly directed toward the starting of a gas turbine having a turbine starter.

Turbine starters are Well known, having been used extensively for the starting of internal combustion engines and gas turbines, the starter using a gaseous flllld derived from the burning of cordite or similar solid fuel cartridges. It has been found that these cartridges are not entirely satisfactory for the use in starters fitted to certain modern engines in that the engines per se may have a very high inertia requiring a sustained fluid flow through the starter and this the cartridge cannot adequately supply.

It has been suggested that a liquid fluid be employed in the form of a monofuel. By the term monofuel I mean any fuel which does not require external oxygen for decomposition. Such a monofuel, for example, is propyl nitrate (CxHqNOs).

Various technical difliculties are associated with the initiation of the decomposition of a monofuel, and the satisfactory supply of the decomposed fluid to the starter. I have found that the admixture of the monofuel and air ignited by a spark to initiate decomposition is undesirable, unreliable and at times dangerous, and to overcome the disadvantage of such a method I have adopted a method which obviates the need of an admixture of air and monofuel.

According to the present invention I provide apparatus for starting a gas turbine having a turbine starter wherein a main chamber and an auxiliary chamber, provided with a heating means, are in communication one with the other and arranged in series, each adapted to receive liquid monofuel (as hereinbefore defined) the main chamber being provided with an exhaust nozzle, to the turbine starter, having an orifice area related to the requisite flow of fluid to the said turbine starter, the auxiliary chamber having an exhaust nozzle, where it communicates with the main chamber, the orifice area of the nozzle being designed to give such a pressure and temperature in the auxiliary chamber, which has a volume smaller in value than that of the main chamber, that the decomposition of the monofuel occurs in the auxiliary chamber and upon the fluid entering the larger volume of the main chamber it is arranged to be at a temperature and pressure slightly above the basic minimum requisite for decomposition of the said monofuel thereby permitting monofuel to be fed directly to the main chamber for decomposition and thence to the starter turbine, the auxiliary chamber and its heating means may then be shut off, if desired.

It is a feature of the invention that the heating means of the auxiliary chamber may comprise an electric heater coil and adapted to be open-circuited as soon as the monofuel is decomposing satisfactorily within the main chamber.

It is a further feature of the invention that the heating means of the auxiliary chamber may be an electric spark; since the energy associated with the spark will be low 2,775,866 -Patente'd Jan. 1, 1957 ice I envisage theuse of accurately controlled switching rneans for-the-timing 'of-the fuel ingress and egress to thesaidtauxiliary chamber with the instant of spark. Furthen' the shape of'the. auxiliary chamber will be critical to ensurecomplete decomposition of the monofuel andranelongated auxiliary chamber may be preferable to ensure that the monofuel may be sprayed'intothe auxiliary c'hamb'er and remain in the hot zone for a suitableperiod-of time.

It-is -yet a further feature of the invention that the auxiliarychamber may be housed within the main cham ber.

It war-be. appreciated that decided advantages accrue f-rom -the use of acOil hea'ting means within the auxiliary chamber in that the coil is only in the hot zone of the auxiliary chamber for a small period of time; whereas if it were placed in the main chamber it would be in the hot zone of the main chamber for the entire period of the starting operation, and this would have a deleterious effect upon the coil.

This application is a division of application Serial No. 291,618, filed June 4, 1952.

One embodiment of the invention is now described by way of example only, reference being had to the accompanying schematic diagram. The main chamber A with an auxiliary chamber B in series, and a communicating pipe D is adapted to be supplied with monofuel from a branched supply pipe E, E1 through inlet spray nozzles F, F1. A heater coil G, the electrical supply being not shown, is provided within the auxiliary chamber B. It will be noted that the volume of auxiliary chamber B is only a fraction of the volume of the main chamber A. Two exhaust nozzles H, H]. are provided, the nozzle H permitting fluid to pass from auxiliary chamber B to main chamber A, while nozzle H1 permits fluid to pass from the main chamber A to the starter turbine C. Using monofuel with assumed basic minimum decomposition values of lbs. per square inch and 400 C. (to facilitate description of the invention) the nozzle H1 is arranged to have an orifice area (say 8 mm.) able to provide the starter turbine C with the requisite flow of fluid. The conditions in the main chamber A during normal starting conditions must be the stated basic minimum values of pressure and temperature, that is to say 100 lbs. per square inch and 400 C. to ensure decomposition of the monofuel coming in at spray nozzle F. A high pressure of about 1600 lbs. per square inch is considered desirable but not necessarily essential for the conditions in the auxiliary chamber to ensure substantially instantaneous decomposition of monofuel coming in at the spray nozzle F1. The orifice area of the exhaust nozzle H is related to that of the exhaust nozzle H1 in an inverse ratio to the pressures of their respective chambers; in this case the nozzle orifice I-I would be 2 mm. in that the pressures are in the ratio of 16:1 and the nozzle diameters are consequently in a ratio of 4:1. The temperature of the fluid exhausting from nozzle H into the main chamber A is, for example, about 1000 C. The operation is as follows: Monofuel is supplied to spray nozzle F1 and nozzle F is shut off, decomposition of the fuel occurs in auxiliary chamber B due to the heat from the heater coil G. Decomposed fuel in fluid form enters main chamber A along the communicating pipe D and, on entering the increased volume of the main chamber, is reduced to the basic minimum conditions of pressure and temperature for the monofuel or slightly above this. The fuel is now fed from the spray nozzle F and spray nozzle F1 may be shut oflf, the coil G being open-circuited. Decomposition of the fuel now takes place in main chamber A and fluid passes through the exhaust nozzle H to the starter turbine C, and, as will be appreciated, a sustained flow of fuel is easily maintained to provide an effective start for an engine having high inertia.

What I claim as new and desire to secure by Letters Patent of the United States is:

In apparatus for starting a prime mover, the combination comprising, a prime mover starter mechanism provided with a gas inlet, a first chamber having an inlet and an outlet, means for delivering through said first chamber inlet a spray of a monofuel which exothermically decomposes under elevated temperature and pressure conditions, heating means for said first chamber to raise the temperature thereof to initiate decomposition of the monofuel sprayed therein by which decomposition a gaseous pressure results at temperatures in excess of the minimum required to effect self-sustained decomposition of the monofuel, a second chamber having an inlet and outlet which chamber is provided with a greater volumetric capacity than said first chamber, means for de livering through said second chamber inlet a spray of said monofuel, conduit means connecting the outlet of said first chamber with the inlet of said second chamber through which flows gas at temperatures and pressures in excess of the minimum requirements to effect decomposition of the monofuel delivered to said second chamber, and conduit means connecting said outlet of the second chamber with the gas inlet of said starter mechanism through which gas flows to efiect starting of the prime 10 mover.

References Cited in the file of this patent UNITED STATES PATENTS 

